Re: [rtcweb] JSEP: Why always offer actpass?

Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com> Thu, 04 December 2014 13:57 UTC

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From: =?utf-8?B?U3RlZmFuIEjDpWthbnNzb24gTEs=?= <stefan.lk.hakansson@ericsson.com>
To: Christer Holmberg <christer.holmberg@ericsson.com>, Justin Uberti <juberti@google.com>
Thread-Topic: [rtcweb] JSEP: Why always offer actpass?
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Date: Thu, 4 Dec 2014 13:57:42 +0000
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Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] JSEP: Why always offer actpass?
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On 04/12/14 14:43, Christer Holmberg wrote:
> What about the following text:
>
> 8.3.2.  TLS Role Determination
>
>     If the m- line proto field value is 'SCTP/DTLS' or 'DTLS/SCTP', the
>
>     SDP setup attribute [RFC4145] is used to determine the 'active/
>
>     passive' status of the offerer and answerer.  The 'active/passive'
>
>     status will be used to determine the TLS roles, following the
>
>     procedures in [RFC4572] (the 'active' endpoint will take the TLS client
>
>     role).
>
>     Once a DTLS connection has been established, if the 'active/passive'
>
>     status of the endpoints change during a session, a new DTLS
>
>     connection MUST be established.  Therefore, endpoints SHOULD NOT
>
>     change the ‘active/passive’ status in subsequent offers and answers,

Did not the discussion (for rtcweb) conclude that subsequent offers 
should offer actpass, but that subsequent answers must say the same as 
the previous answer?

>
>     unless they want to establish a new DTLS connection (in which case
>
>     the new 'active/passive' status of the offerer and answerer will be
>
>     used to determine the TLS roles associated with the new DTLS
>
>     connection).
>
>     NOTE: The procedure above is identical to the one defined for SRTP-
>
>     DTLS in [RFC5763].
>
> Regards,
>
> Christer
>
> *From:*rtcweb [mailto:rtcweb-bounces@ietf.org] *On Behalf Of *Christer
> Holmberg
> *Sent:* 4. joulukuuta 2014 8:55
> *To:* Justin Uberti
> *Cc:* rtcweb@ietf.org
> *Subject:* Re: [rtcweb] JSEP: Why always offer actpass?
>
> I’ve missed that. Awesome! :)
>
> So, if we’re ok with that approach, then we should use similar text in
> the SCTP-SDP draft.
>
> Regards,
>
> Christer
>
> *From:*Justin Uberti [mailto:juberti@google.com]
> *Sent:* 4. joulukuuta 2014 8:53
> *To:* Christer Holmberg
> *Cc:* Stefan Håkansson LK; Makaraju, Maridi Raju (Raju); Roman Shpount;
> rtcweb@ietf.org <mailto:rtcweb@ietf.org>
> *Subject:* Re: [rtcweb] JSEP: Why always offer actpass?
>
> 5763, S 6.6 seems to imply that:
>
>   Note that if the active/passive status of the endpoints changes, a new
>
>   connection MUST be established.
>
> On Wed, Dec 3, 2014 at 10:30 PM, Christer Holmberg
> <christer.holmberg@ericsson.com <mailto:christer.holmberg@ericsson.com>>
> wrote:
>
> Hi,
>
> So, one suggestion would be to say that, IF one (there offerer or
> answerer) changes the previously negotiated roles, the DTLS connection
> MUST be re-established – even if the transport parameters etc aren’t
> changed. I think that would be a very useful clarification.
>
> Regards,
>
> Christer
>
> *From:*Justin Uberti [mailto:juberti@google.com
> <mailto:juberti@google.com>]
> *Sent:* 4. joulukuuta 2014 7:49
> *To:* Christer Holmberg
> *Cc:* Stefan Håkansson LK; Makaraju, Maridi Raju (Raju); Roman Shpount;
> rtcweb@ietf.org <mailto:rtcweb@ietf.org>
>
>
> *Subject:* Re: [rtcweb] JSEP: Why always offer actpass?
>
> Currently, Chrome errors out (i.e. setRD fails).
>
> However, I suspect that teardown of the old DTLS association and setup
> of a new DTLS association is the desired behavior.
>
> On Wed, Dec 3, 2014 at 8:34 PM, Christer Holmberg
> <christer.holmberg@ericsson.com <mailto:christer.holmberg@ericsson.com>>
> wrote:
>
> Hi,
>
> Issue #72 talks about maintaining the previously negotiated role when
> actpass is received. I think that is a good approach, and could be used
> in Offer/Answer too.
>
> BUT, what does the browser do if e.g. the previous role is passive and
> active is received?
>
> Regards,
>
> Christer
>
> Sent from my Windows Phone
>
> ------------------------------------------------------------------------
>
> *From: *Stefan Håkansson LK <mailto:stefan.lk.hakansson@ericsson.com>
> *Sent: *‎03/‎12/‎2014 17:48
> *To: *Justin Uberti <mailto:juberti@google.com>
> *Cc: *Makaraju, Maridi Raju (Raju)
> <mailto:Raju.Makaraju@alcatel-lucent.com>; Christer Holmberg
> <mailto:christer.holmberg@ericsson.com>; Roman Shpount
> <mailto:roman@telurix.com>; rtcweb@ietf.org <mailto:rtcweb@ietf.org>
> *Subject: *Re: [rtcweb] JSEP: Why always offer actpass?
>
> On 01/12/14 18:26, Justin Uberti wrote:
>>
>>
>> On Sun, Nov 30, 2014 at 7:26 AM, Stefan Håkansson LK
>> <stefan.lk.hakansson@ericsson.com <mailto:stefan.lk.hakansson@ericsson.com>
>> <mailto:stefan.lk.hakansson@ericsson.com>> wrote:
>>
>>     On 30/11/14 16:06, Makaraju, Maridi Raju (Raju) wrote:
>>      >> On 30/11/14 14:51, Makaraju, Maridi Raju (Raju) wrote:
>>      >>>> Hi,
>>      >>>>
>>      >>>>>> RFC 7345 (UDPTL-DTLS) says the following:
>>      >>>>>>
>>      >>>>>> "Once an offer/answer exchange has been completed, either
>>      >>>>>> endpoint
>>      >>>> MAY
>>      >>>>>> send a new offer in order to modify the session.  The
>>      >>>>>> endpoints
>>      >>>> can
>>      >>>>>> reuse the existing DTLS association if the key fingerprint
>>      >>>>>> values
>>      >>>> and
>>      >>>>>> transport parameters indicated by each endpoint are unchanged.
>>      >>>>>> Otherwise, following the rules for the initial offer/answer
>>      >>>> exchange,
>>      >>>>>> the endpoints can negotiate and create a new DTLS association
>>      >>>>>> and, once created, delete the previous DTLS association,
>>      >>>>>> following the same rules for the initial offer/answer exchange.
>>      >>>>>> Each endpoint needs to be prepared to receive data on both the
>>      >>>>>> new and old DTLS associations as long as both are alive."
>>      >>>>>>
>>      >>>>>> So, I guess that can be read in a way that the setup attribute
>>      >>>>>> as such
>>      >>>> does not impact previously
>>      >>>>>> negotiated TLS roles - unless the key fingerprint values and/or
>>      >>>>>> transport
>>      >>>> parameters are modified.
>>      >>>>>>
>>      >>>>>> The SCTP-SDP draft currently says that a subsequent offer must
>>      >>>>>> not change
>>      >>>> the previously negotiated roles. But, I guess
>>      >>>>>> we could say something similar as in RFC 7345.
>>      >>>>>
>>      >>>>> I have struggled with this language quite a bit from the
>>      >>>>> implementation
>>      >>>> perspective. I think we need to explicitly state
>>      >>>>> that endpoints MUST reuse the existing association if the key
>>      >>>>> fingerprint
>>      >>>> values and transport parameters indicated
>>      >>>>> by each endpoint are unchanged.
>>      >>>>
>>      >>>> We could take such general approach.
>>      >>>>
>>      >>>> However, for 'SCTP/DTLS' (DTLS over SCTP), I assume that the DTLS
>>      >>>> connection will also be re-established if the underlying SCTP
>>      >>>> association is re- established - even if no transport parameters
>>      >>>> etc are changed.
>>      >>>>
>>      >>>> Also, RFC 6083 says:
>>      >>>>
>>      >>>> "Each DTLS connection MUST be established and terminated
>>     within the
>>      >>>> same SCTP association."
>>      >>>>
>>      >>>>
>>      >>>>> The way this language reads to me is that endpoints can reuse the
>>      >>>>> existing
>>      >>>> association if they want to, but they can create a new one if they
>>      >>>> don't. Also, when this new
>>      >>>>> association is created, it is unclear if old setup roles MUST be
>>      >>>>> preserved
>>      >>>> or if they MUST be selected based on the current offer/answer
>>      >>>> exchange. It seems the current
>>      >>>>> specification language is not strong or clear enough on this
>>      >>>>> topic.
>>      >>>>
>>      >>>> In my opinion, IF a new DTLS connection needs to be established
>>      >>>> (for whatever reasons), the current roles should be used.
>>      >>>
>>      >>> <Raju> When ICE is NOT used, how does the offerer know that the
>>      >>> answerer does not change the fingerprint and/or transport
>>     parameters?
>>      >>> I guess it does not know. So, offerer has to be prepared for
>>     new DTLS
>>      >>> association by offering actpass. When ICE is used, the answerer
>>     can't
>>      >>> change transport parameter unless offerer does ICE restart (which
>>      >>> changes offerer transport parameters); Ref [1] is very clear on
>>     this
>>      >>> indicating "DTLS handshake procedure is repeated". However,
>>     even when
>>      >>> ICE is used, I do not find any restriction about answerer not
>>      >>> changing fingerprint. So, even without ICE restart answerer can
>>      >>> trigger a DTLS renegotiation by changing its fingerprint.
>>      >>>
>>      >>> To conclude all this, IMO whether ICE is used or not, sending
>>     actpass
>>      >>> for all new offers may be cover all possible scenarios.
>>      >>
>>      >> That is also my conclusion based on the discussion so far.
>>      >>
>>      >> I also think the JSEP draft as far as detailed out is correct,
>>     but info
>>      >> about how the implementation should behave for Subsequent answers is
>>      >> missing. Text saying that the role must be maintained (unless
>>     there is
>>      >> an ICE restart) should be put in there.
>>      >
>>      > <Raju>
>>      > Hi Stefan,
>>      > Looks like, there is some misunderstanding here.
>>
>>     Probably my fault in that case :)
>>
>>     > My conclusion is to include
>>     > actpass, but not the previously negotiated role, in all subsequent offers,
>>     > not just during ICE-restarts.
>>
>>     I think that is what the JSEP draft says - and my conclusion is that it
>>     _is_ correct.
>>
>>     My point was that the _answer_ should (when it is a subsequent answer)
>>     should say the same role as in previous answers (unless there is an ICE
>>     restart).
>>
>> I agree the JSEP text should indicate that roles should stay the same.
>> We have had this as a TODO for a while:
>>https://github.com/rtcweb-wg/jsep/issues/72
>
> Great. I should have checked that out before.
>